1. Field of the Invention
The present invention relates to a Raman amplifier Raman-amplifying signal light of a plurality of channels having wavelengths different from each other, and an optical communication system including the same.
2. Related Background Art
A rare earth element-doped optical fiber amplifier which uses a rare earth element-doped optical fiber as an optical amplification medium is an optical device having a structure for supplying pumping light having a wavelength to pump the rare earth element into the optical fiber, and amplifying signal light by using the transition between the energy levels of the rare earth element. Therefore, in a rare earth element-doped optical fiber amplifier, the wavelength band range of signal light which can be amplified is limited. Whereas the Raman amplifier is an optical amplifier using the Raman scattering phenomena in an optical fiber where signal light propagates, and if the transmission medium of the signal light is a silica-based optical fiber, then the signal light can be Raman-amplified by supplying pumping light, having a wavelength about 100 nm shorter than the signal light wavelength, to the optical fiber. Therefore, with the Raman amplifier, the wavelength band range of signal light which can be amplified is arbitrary, and the pumping light wavelength can be appropriately set according to the signal light wavelength.
As the Raman amplifier, not only a structure for Raman-amplifying signal light in an optical fiber transmission line laid in the relay section, but also a structure, as a module provided in a repeater, for Raman-amplifying signal light in the repeater is known. The Raman amplifier is an optical device using Raman scattering, which is one type of non-linear optical phenomena in a Raman amplification optical fiber. Since a dispersion compensating optical fiber compensates for a chromatic dispersion of the optical fiber transmission line is, in general, an optical fiber having a small effective area and a high non-linearity, a structure for Raman-amplifying signal light by using this dispersion compensating optical fiber as a Raman amplification optical fiber is also known.